Generally, Internet Protocol (IP) Multimedia Subsystem (IMS) or Multimedia Domain (MMD) provides messaging services in which users can exchange IP-based user messages with each other.
The ‘message’ as used herein means text or multimedia application layer data exchanged between users, or User Equipments (UEs), of IMS. The message may include a Session Initiation Protocol (SIP) message, meaning the data exchanged over an SIP session to deliver signaling information used in the messaging service, and a Message Session Relay Protocol (MSRP) message, meaning the data exchanged over an MSRP session to actually deliver a user message.
A messaging service provided in IMS may include ‘instant messaging’ and ‘session (or SIP)-based messaging service’. The instant messaging is a scheme for delivering a short message or a short media message over an SIP message. In this case, because the instant messaging directly uses an SIP message and does not separately form (or establish) an MSRP session, it does not form an SIP session used for forming an MSRP session, as well. However, the session-based messaging service is used for continuous message exchange. In this case, because each message is delivered over an MSRP message other than the SIP message, there is a need for an SIP session used for generating the MSRP session.
FIG. 1 is a diagram illustrating a network configuration for message delivery in the general IMS.
In IMS, a core network (CN) can be divided into a Call Session Control Function (CSCF) block and a Home Subscriber Server (HSS) block according to function.
The CSCF block performs a call/session processing-related function, and is divided into Proxy CSCF (P-CSCF) #1 115a and #2 115b, Integrating CSCF (I-CSCF) #2 125, and Serving CSCF (S-CSCF) #1 120a and #2 120b according to their function.
The P-CSCF#1 115a and P-CSCF#2 115b are elements serving as a gateway when a UE first accesses the network to receive an IMS service, and they serve as proxy and User Agent (UA). Basically, they relay SIP messages between the UE and the network. The I-CSCF#2 125 serves as a contact for all incoming calls to connect with a subscriber in the network, and routes a call by inquiring of the HSS for location detection of a terminating (or called) subscriber. In addition, because the I-CSCF#2 125 serves as a gateway to another IMS network, it can also serve as a firewall for hiding topology in the network for security. The S-CSCF#1 120a and the S-CSCF#2 120b each perform a registration function to the corresponding network and various authentication functions necessary therefor. That is, for provisioning of various multimedia services, the S-CSCF#1 120a and the S-CSCF#2 120b each perform a series of mechanisms of directly interworking with application servers, routing a call based on triggering information, and providing the services.
Referring to FIG. 1, a UE#1 100 delivers an SIP message for forming an SIP session, to the P-CSCF#1 115a, a first contact point of an external network where it is currently located, via a Radio Access Network (RAN) #1 105a (see 11).
The P-CSCF#1 115a searches for a home network B of the UE#1 100, and delivers the SIP message to the S-CSCF#1 120a of the home network B (see 12).
The S-CSCF#1 120a searches for a home network C of a UE#2 110 to which the UE#1 100 desires to form an SIP session. The SIP message delivered by the S-CSCF#1 120a, if it enters the home network C, is preferentially delivered to the I-CSCF#2 125 (see 13), and then delivered to the S-CSCF#2 120b of the home network C via the I-CSCF#2 125 (see 14).
The S-CSCF#2 120b searches for an external network D where the UE#2 110 to which it provides the service is currently located, and delivers an SIP message to the P-CSCF#2 115b of the external network D (see 15). Finally, the UE#2 110 receives the SIP message delivered via the RAN#2 105b (see 16).
Through the processes 11 through 16, the UE#1 100 and the UE#2 110 exchange SIP messages with each other, thereby establishing an SIP session. On the contrary, if the SIP message is delivered from the UE#2 110 to the UE#1 100, the message delivery is achieved in the reverse order of the processes 11 through 16.
MSRP is a text-based connection-oriented protocol for exchanging arbitrary Multipurpose Internet Mail Extension (MIME) contents, especially instant messages. MSRP can deliver the entire message in one complete unit, or can deliver the message in several divided chunk units.
An MSRP session is formed over an SIP session. The information necessary for forming the MSRP session, including MSRP URL addresses and ports of the UE#1 100 and UE#2 110, and media characteristics of the MSRP message to be delivered over the MSRP session, is delivered over Session Description Protocol (SDP) of the SIP message. Actually, the user data is delivered over a separate MSRP session from the SIP session. While the SIP session is formed via CSCFs, the MSRP session is formed by means of general Transmission Control Protocol (TCP) connection.
MSRP has two request types: ‘SEND’ and ‘REPORT’. SEND is for sending one complete message, or sending a part, or a chunk, of the complete message, and REPORT is for sending state information of a previously sent message, or sending a byte range of the message.
FIG. 2 is a diagram illustrating a procedure for forming an MSRP session for sending a general instant message.
Referring to FIG. 2, in step 215, a UE#1 200 generates its own MSRP URL in SDP, and sends an SIP INVITE message containing the SDP to a UE#2 210. For example, the INVITE message can be expressed as ‘a=path:msrp://UE#1pc.example.com:7777/iau39;tcp’.
In step 220, the UE#2 210 generates its own MSRP URL in SDP, and sends an SIP 200 OK message containing the SDP to the UE#1 200. For example, the 200 OK message can be expressed as ‘a=path:msrp://bob.example.com:8888/9di4ea;tcp’.
In step 230, the UE#1 200 sends a SIP ACK message, a response to the 200 OK message, to the UE#2 210, and sets up TCP connection. Thereafter, in step 240, the UE#1 200 sends a particular message to the UE#2 210 over an MSRP SEND message. For example, the MSRP SEND message can be expressed as follows.
  ′MSRP d93kswow SEND    To-Path: msrp://UE#2.example.com:8888/9di4ea;tcp    From-Path:msrp://UE#1pc.example.com:7777/iau39;tcp    Message-ID: 12339sdqwer    Content-Type: text/plain    Hi, I'm UE#1!  -------d93kswow$′
After receiving the MSRP SEND message in step 240, the UE#2 210 responds to the UE#1 200 with an MSRP 200 OK message in step 245. In step 250, the UE#2 210 sends an instant message containing a particular message to the UE#1 200 over an MSRP SEND message. For example, the instant message can be expressed as follows.
′MSRP dkei38sd SEND To-Path: msrp://alicepc.example.com:7777/iau39;tcp From-Path: msrp://bob.example.com:8888/9di4ea;tcp Message-ID: 456 Content-Type: text/plain Hi, UE#1! I'm UE#2! -------dkei38sd$′
After receiving the instant message in step 250, the UE#1 200 responds to the UE#2 210 with an MSRP 200 OK message in step 255. In step 260, the UE#1 200 sends a SIP BYE message indicating the completion of the message transmission. In step 265, the UE#2 210 sends a 200 OK message, a response thereto, closing the SIP session. Thereafter, the MSRP session is also closed, ending the instant messaging service.
Assume that the UE#1 200 and the UE#2 210 transmit data during messaging service. In this case, when the data transmitted using an MSRP session is too large in size, the standard defines that the UEs should divide the data into chunks before transmission.
Therefore, the foregoing conventional IMS-based messaging service is inefficient, because it may suffer from overload if the MSRP message exchanged between the UE#1 200 and the UE#2 210 is divided into chunks. That is, data throughput for the existing chunk units has not been defined, causing a considerable delay during the actual service and resulting in a waste of the expensive wireless resources.